CO2Stats Project
http://www.maxtility.com/co2stats/

The CO2Stats Project freely distributes a widget that calculates your web site or blog’s carbon footprint in real-time due to the total electricity usage of your readers’ computers as they spend time on your site. You can then offset your popularity by buying carbon credits. Founded by Ph.D. students at Harvard and Yale, The CO2Stats Project has the ambitious goal of making the entire Web carbon neutral! This has been added to the tools section of Research Resources Subject Tracer™ Information Blog.